Kras is one of ras genes that undergo mutation in various cancers. Mutations are frequently limited to only one of the ras genes, and the frequency is tissue- and tumor type-specific. Ras-binding domains/Ras-associating domains (RBD/RAD) are the primary Ras-binding sites in Ras effector proteins. Raf-1 is a pivotal effector of Ras. Among the Ras family members, it is preferentially activated by KRAS, showing that its RBD predominantly interacts with KRAS.